With the advance of modern electronics technology, the overall electronics size becomes smaller while the size of a resonance antenna is constrained to its wavelength in a quarter or a half wavelength at a given frequency, often resulting in the largest part of a wireless system being its antenna. A microstrip patch antenna is one of the most popular resonance antennas due to its light weight and easy fabrication and therefore widely used for many commercial electronic devices such as GPS receivers and for military applications such as airborne and aerospace communication. It is usually composed of a metallic patch and a ground plane with a dielectric layer sandwiched in between. Because of the simple structure, a patch is easy to fabricate using standard PCB fabrication techniques, making it suitable for low cost and mass production.